Study On Sensing Of Whispering Gallery Mode/Random Microcavity Laser Based On Wet Etching

Since the 21 st century,the human society has been greatly promoted by the rapid development of laser technology.Higher demands for the performance,size and cost of lasers have also been required.As a new member of the laser family,the traditional resonators of microcavity laser were replaced by optical microcavities(Fabry-Perot cavity,distribute feedback microcavity,whispering gallery mode microcavity(WGM)microcavity and random scattering cavity),which achieved the miniaturization and integration of laser size to a great extent and improved the performance of laser devices.In particular,taking advantage of its ultra-small size and ultra-high sensitivity,the application of microcavity laser in the field of sensing,not only can realize the detection of pressure,temperature,humidity and sound and other physical signals,but also can be applied to environmental molecular monitoring,single virus detection and protein detection in the field of biomedicine.In the context of global warming and COVID-19,both social economic development and people’s health have been facing new challenges.Higher performance and application scenarios of microcavity laser sensing have also been required.However,the existing sensor applications based on microcavity laser,especially the sensor based on whispering gallery mode microcavity laser and random laser,were still in the laboratory stage,and there have been still many problems to be explored.Among them,the following three problems were the focus of this thesis:(1)The fabrication process of microcavity laser was complex and costly.It still cannot be separated from the laboratory to meet the needs of the market.Therefore,the simplification and cost reduction of the fabrication process of optical microcavity has become an important topic and attracted significant attention.(2)Although microcavity lasers have many advantages in terms of spatial size and sensitivity,more kinds of microcavities and materials were still needed to be developed to improve the portability of the microcavity lasers as well as meet the sensing requirements of the microcavity lasers in more application scenarios.(3)Different kinds of microcavity laser were expected to be integrated in a compound cavity to further improve the integration degree of microcavity lasers,which was of great significance to the application of microcavity lasers in the future.In view of the above problems,the main research contents and innovations of this thesis are as follows:(1)An ultrathin-film microring laser was fabricated using inkjet printing and a wet etching lift-off technique.Whispering-gallery-mode lasing was observed under optically pumped conditions in the film.The freestanding laser can be transferred to arbitrary surfaces for multifunctional applications,such as acoustic and relative humidity sensing.Using the first eigenmode of a membrane vibration,an acoustic sensor with a 0.15 Pa limit of detection was demonstrated via laser bandwidth broadening.A relative humidity sensor with a 1.1% limit of detection via wavelength shifts was demonstrated by placing the device on an optical fiber facet.These costeffective,transferrable,multifunctional laser sensors will have many additional applications.(2)A silicon nanowire array was grown by a metal-assisted chemical etching method.A colloidal quantum dot solution was spin-coated on silicon nanowires to form the random laser.The performance of the random laser was controlled by the resistivity of silicon wafers and the length of silicon nanowires.A transition from incoherent random lasing to coherent random lasing was obtained by increasing the resistivity of the silicon wafers.The random lasing threshold increased with an increase in the length of the silicon nanowires.These results may be useful to explore high-performance silicon-based random lasers.(3)A compound cavity was proposed to achieve both whispering gallery mode(WGM)lasing and random lasing.The WGM-random compound cavity consisted of a random structure with an annular boundary,which was fabricated by a method combining both the inkjet printing and metal-assisted chemical etching methods.An ultrathin polymer membrane was attached to the WGM-random compound cavity by wet etching lift-off technique,forming a polymer laser device.A transformation from WGM lasing to random lasing was observed under optical pumping conditions.The laser performance could be easily tailored by changing the parameter of the WGMrandom compound cavity.These results provide a new avenue for the design of integrated light sources for sensing applications.